This invention relates to an ignition system for an internal combustion engine, and more particularly, to a temperature compensating circuit for the ignition system of an internal combustion engine.
In a conventional ignition system for an internal combustion engine in which an alternating signal produced in timed relationship with engine rotation is produced in a pickup coil and applied to a detecting means which controls a switching means to produce or interrupt current through an ignition coil, an N-P-N transistor or a P-N-P transistor are used as the detecting means for the alternating signal and the detecting level (threshold level) for the alternating signal is determined by the voltage drop of the base to emitter path of the transistor. Since this voltage drop varies with changes in ambient temperature, the detecting condition of the transistor is effected by the temperature. A diode has been used for compensating the detecting condition of the transistor for variations in temperature; however, the diode consumes considerable energy of the alternating signal in producing a voltage drop which varies with the temperature in such a way as to shift the detecting level to compensate for the temperature effects of the detecting transistor. During low speed engine rotation, the energy of this alternating signal is very small, and, therefore, it is impossible to apply an alternating signal of sufficient energy to the detecting means during such operation due to the power consumption of this diode.
It is an object of this invention to provide an improved ignition system for an internal combustion engine.
It is a further object of this invention to provide an improved ignition system for an internal combustion engine in which a diode for compensating temperature effects of an alternating signal detecting means is not required.
It is another object of this invention to provide an ignition system having improved low speed operating characteristics.
In accordance with this invention, a detecting means for an alternating signal includes a circuit in which a P-N-P transistor and an N-P-N transistor are associated with each other so that the temperature effects of the base to emitter paths of these transistors compensate each other. Therefore, the detecting means operates independent of temperature in response to the alternating input signals with the result that current through the ignition coil is controlled more perfectly.